Let me be clear: no political scientist that I know of believes that “debates don’t matter” (although I don’t doubt that a cursory or short-hand reading of some of their comments may lead one to believe this.) Instead, what they argue is that the persuasive impact of debates is small, and therefore debates themselves are rarely consequential in terms of independently altering the outcome of an election. But this is different from saying they don’t matter. In fact, debates do matter. I have argued that the first presidential debate served as a focusing event, allowing many voters to make a side-by-side comparison of the two candidates for the first time. In so doing, a small number of viewers may have been persuaded that Mitt Romney is not nearly as extreme as he was being portrayed by the Obama campaign, and that given the economic fundamentals driving this campaign, they might take a chance on the challenger. In short, the debate accelerated a process that was already underway, in which polls, particularly at the state level, moved closer into alignment with what the fundamentals driving the vote dictated.

But notice that I said a small number of viewers. For all the talk about what a disaster the first debate was for Obama, the impact on his polling support was not very large. Middlebury College student Anna Esten, building on research by political scientist Tom Holbrook regarding the impact of previous debates, calculates that Obama lost 2.7% support nationally after the first debate. (She based this on a comparison of the average of national polls in the field in the week before the debate with the average of polls in the week after.) As you can see in the chart below, which incorporates Holbrook’s data, Obama’s 2.7% drop is relatively large impact for a first debate – about .5% larger than the second biggest – but not overwhelmingly so.

Incumbent Party Percent of Two-Party Vote During Debate Periods, 1988 to 2008

For a variety of reasons, however, I would not expect tomorrow’s debate to have nearly the impact of the first presidential debate, or even the second one, for that matter. First, and I don’t want to make too much of this given the small “n”, the average impact of the four third debates dating back to 1992 on the incumbent party’s polls is a miniscule -.10. That compares to -1.19 for the first debate, and -.24 for the second. Second, tomorrow’s debate centers on foreign policy. This is a topic much in the news of late due to the controversy over the killing of a U.S. diplomat and his security team in Benghazi, and more recently the reports – denied by the White House – that Iran has agreed to bilateral talks with the U.S. regarding its nuclear program. Nonetheless, most polls indicate that voters’ concerns over the economy far outweigh their interest in foreign policy questions. Finally, we have had two relatively widely viewed debates so far, with the audience for the second, at an estimated 65.6 million viewers, only slightly smaller than the 67 million who tuned into the first debate. (This does not count the millions more who viewed the debates through other means, such as computers and tablets.) I expect that the audience for tomorrow’s debate will be smaller than that for the first debate – and perhaps even less than the second, since it will be occurring opposite Monday night football. And there likely will be fewer undecided voters within the viewing audience. Finally, with the election polls now more in line with where I have been predicting they would be since Labor Day, I think there is likely to be a bit less volatility in the polling in the remaining 17 days before the Election.

Again, this is not to say that Monday’s debate “won’t matter.” It should help at least some of the remaining undecideds begin considering their vote choice in light of the fundamentals, and in this regard should continue the process of bringing the polling closer in line with the actual vote come November 6. But I would be very surprised if it led to a bump, or slide, in Obama’s polling anywhere near the 2.7% impact of the first debate.

That doesn’t mean it won’t be entertaining, however! As always, I’ll be on, live blogging, and yes, the live blogging software is now installed and operating properly. (Really. I mean it.) So join in. It’s scheduled to start at 9, and I’ll be on slightly before.

And, remember, you can’t ever be sure who is watching the debate, and what they will learn (hat tip to Kate Hamilton)!